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an organism (especially a bacterium) that does not require air or free oxygen to live

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嫌(けん)気性生物(空気・遊離酸素を必要としない細菌類)

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/11/27 17:28:46」(JST)

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Aerobic and anaerobic bacteria can be identified by growing them in liquid culture:
1: Obligate aerobic (oxygen-needing) bacteria gather at the top of the test tube in order to absorb maximal amount of oxygen.
2: Obligate anaerobic bacteria gather at the bottom to avoid oxygen.
3: Facultative bacteria gather mostly at the top, since aerobic respiration is the most beneficial one; but, as lack of oxygen does not hurt them, they can be found all along the test tube.
4: Microaerophiles gather at the upper part of the test tube but not at the top. They require oxygen but at a low concentration.

5: Aerotolerant bacteria are not affected at all by oxygen, and they are evenly spread along the test tube.

An anaerobic organism or anaerobe is any organism that does not require oxygen for growth. It could possibly react negatively and may even die if oxygen is present. Most such species are unicellular microbes, though some are near-microscopic metazoa and some deep-sea worms. Some largely unicellular anaerobic microbes are protists, but most of the anaerobic microbes are bacteria or Archaea. For practical purposes there are three categories:

obligate anaerobes, which cannot use oxygen for growth and are even harmed by it
aerotolerant organisms, which cannot use oxygen for growth, but tolerate the presence of it
facultative anaerobes, which can grow without oxygen but can utilize oxygen if it is present

In human beings these organisms are usually found in gastrointestinal tract.^[1]

Metabolism

Obligate anaerobes may use fermentation or anaerobic respiration.
Aerotolerant organisms are strictly fermentative.
In the presence of oxygen, facultative anaerobes use aerobic respiration; without oxygen, some of them ferment; some use anaerobic respiration.

Fermentation

There are many anaerobic fermentative reactions.

Fermentative anaerobic organisms mostly use the lactic acid fermentation pathway:

C₆H₁₂O₆ + 2 ADP + 2 phosphate → 2 lactic acid + 2 ATP

The energy released in this equation is approximately 150 kJ per mol, which is conserved in regenerating two ATP from ADP per glucose. This is only 5% of the energy per sugar molecule that the typical aerobic reaction generates.

Plants and fungi (e.g., yeasts) in general use alcohol (ethanol) fermentation when oxygen becomes limiting:

C₆H₁₂O₆ + 2 ADP + 2 phosphate → 2 C₂H₅OH + 2 CO₂↑ + 2 ATP

The energy released is about 180 kJ per mol, which is conserved in regenerating two ATP from ADP per glucose.

Anaerobic bacteria and archaea use these and many other fermentative pathways, e.g., propionic acid fermentation, butyric acid fermentation, solvent fermentation, mixed acid fermentation, butanediol fermentation, Stickland fermentation, acetogenesis, or methanogenesis.

Some anaerobic bacteria produce toxins (e.g., tetanus)

Culturing anaerobes

Since normal microbial culturing occurs in atmospheric air, which is an aerobic environment, the culturing of anaerobes poses a problem. Therefore, a number of techniques are employed by microbiologists when culturing anaerobic organisms, for example, handling the bacteria in a glovebox filled with nitrogen or the use of other specially sealed containers, or techniques such as injection of the bacteria into a dicot plant, which is an environment with limited oxygen. The GasPak System is an isolated container that achieves an anaerobic environment by the reaction of water with sodium borohydride and sodium bicarbonate tablets to produce hydrogen gas and carbon dioxide. Hydrogen then reacts with oxygen gas on a palladium catalyst to produce more water, thereby removing oxygen gas. The issue with the Gaspak method is that an adverse reaction can take place where the bacteria may die, which is why a thioglycollate medium should be used. The Thioglycollate supplies a medium mimicking that of a Dicot, thus providing not only an anaerobic environment but all the nutrients needed for the bacteria to thrive.^[2]

References

^ "Anaerobic bacteria - Overview". http://www.umm.edu/ency/article/003439.htm.
^ "GasPak System". Accessed May 3, 2008.

UpToDate Contents

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English Journal

Nitrate decreases methane production also by increasing methane oxidation through stimulating NC10 population in ruminal culture.

Liu L1, Xu X2, Cao Y1, Cai C1, Cui H1, Yao J1.
AMB Express.AMB Express.2017 Dec;7(1):76. doi: 10.1186/s13568-017-0377-2. Epub 2017 Apr 4.
PMID 28378285

Partial nitritation of stored source-separated urine by granular activated sludge in a sequencing batch reactor.

Chen L1, Yang X1, Tian X1, Yao S1, Li J2, Wang A1, Yao Q3, Peng D3.
AMB Express.AMB Express.2017 Dec;7(1):50. doi: 10.1186/s13568-017-0354-9. Epub 2017 Feb 28.
PMID 28244031

Effect of nitrogen availability on the poly-3-D-hydroxybutyrate accumulation by engineered Saccharomyces cerevisiae.

Portugal-Nunes DJ1, Pawar SS2, Lidén G2, Gorwa-Grauslund MF3.
AMB Express.AMB Express.2017 Dec;7(1):35. doi: 10.1186/s13568-017-0335-z. Epub 2017 Feb 7.
PMID 28176283

Japanese Journal

ヒト腸内グラム陽性細菌の分類の現状 : 嫌気性Phylum FirmicutesおよびPhylum Actinobacteriaを中心に (特集腸内細菌の分類の現状 : 嫌気性菌および乳酸菌を中心に)

腸内細菌学雑誌 30(4), 177-190, 2016-10
NAID 40020999313

教育講演呼吸器感染症における口腔内レンサ球菌と嫌気性菌の役割 (第113回日本内科学会講演会結実する内科学の挑戦 : 今、そしてこれから)

日本内科学会雑誌 105(9), 1796-1802, 2016-09-10
NAID 40020965714

Evaluation of VITEK matrix-assisted laser desorption ionization–time of flight mass spectrometry for identification of anaerobes

Microbiology and immunology 60(7), 477-482, 2016-07
NAID 40020888000

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